dns reverse zone is not working.

hi to all, I've centos64 as one server and second is client and centos 7.5 as two clients.
i am configuring dns in centos 6.4. mine forward zone is working properly gives following output :-

Code:[root@serverora11gr2 Desktop]# dig serverora11gr2.db.net

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.68.rc1.el6_10.3 <<>> serverora11gr2.db.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60891
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;serverora11gr2.db.net. IN A

;; ANSWER SECTION:
serverora11gr2.db.net. 2592000 IN A 192.168.20.50

;; AUTHORITY SECTION:
db.net. 2592000 IN NS serverora11gr2.db.net.

;; Query time: 0 msec
;; SERVER: 192.168.20.50#53(192.168.20.50)
;; WHEN: Sat Oct 26 07:20:49 2019
;; MSG SIZE rcvd: 69all VMs are pinging to each other.

but when i tried to dig reverse zone this shows following error:-
Code:[root@serverora11gr2 Desktop]# dig -x 192.168.20.60

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.68.rc1.el6_10.3 <<>> -x 192.168.20.60
;; global options: +cmd
;; connection timed out; no servers could be reachedmine reverse zone file is :-
Code:$TTL 1D
@ IN SOA serverora11gr2.db.net. root.serverora11gr2.db.net. (
10 ; serial
1D ; refresh
1H ; retry
1W ; expire
3H ) ; minimum
@ IN NS serverora11gr2.db.net.
50 IN PTR serverora11gr2.db.net.
60 IN PTR server75.db.net.
70 IN PTR centos75client.db.net.
80 IN PTR centos64client.db.net.

also host command is working fine:-
Code:[root@serverora11gr2 named]# host serverora11gr2.db.net
serverora11gr2.db.net has address 192.168.20.50
[root@serverora11gr2 named]# host server75.db.net
server75.db.net has address 192.168.20.60how to get reverse zone work